Valve control for reciprocating piston drive with rapidly starting piston stroke



March 4, 1969 A. P. LINZ 3,430,540

VALVE CONTROL FOR RECIPRUCATING PISTON DRIVE WITH RAPIDLY STARTINGPISTON STROKE Filed Oct. 24, 1966 Kfz 7 l li l+ l United States Patent 4Claims ABSTRACT OF THE DISCLOSURE A valve control for a fluid pressureactuated cylinder in which the stroke of the cylinder piston in at leastone direction is rapidly started by suddenly unloading the cylinderchamber on one side of the piston only after the cylinder chamber on theother side of the piston is prepressurized to obtain a rapid pistonstroke in the direction of the unloaded cylinder chamber.

This invention relates to a valve control for reciprocating pistondrives with a rapidly starting piston stroke, especially for miscutdevices on flying shears, in order to bring one cutting knife during theoperation of the shears into and out of the operating position relativeto the other cutting knife. This control arrangement may further beapplied advantageously to all piston drives in which the amount ofswitching time required by a slide valve may constitute a problem.Furthermore, the invention is not limited to a particular pressuremedium since the piston drive may be operated hydraulically orpenumatically. It may also comprise a straight-through piston shaft or ashaft of smaller length.

This invention incorporates the principle of preenergization which is incommon use in electrical engineering, and proposes a valve control forreciprocating piston drives in which at least one cylinder chamber, inparticular the cylinder chamber which is to be unloaded or relieved toexecute a rapid starting piston stroke, is associated with a return lineincluding a relief valve which may be opened at will, and a feedingvalve arranged parallel to the relief valve and connected to thepressure line, and that the other cylinder chamber may be putindependently under pressure over a slide valve. This slide valve,through which the pressure medium flows during the fast piston stroke,may now be opened already before the piston stroke is to be started ifthe controlled relief valve in the return line associated with thecylinder chamber to be unloaded and the parallel connected feeding valvein the pressure line are closed.

The piston drive is thus pre-energized in the desired direction by meansof the driving pressure because the cylinder chamber to be unloaded isstill closed. The switching time of the pre-opened slide valve lieswithin the period before the desired starting of the piston stroke. Thepressure line is under pressure so that the influence of the expansionof the pressure line to provide the speed at the start of the pistonstroke is eliminated.

The piston stroke is started or actuated in that the controlled reliefvalve in the return line of the cylinder chamber to be unloaded isopened. While normally a piston stroke is initiated by opening a valveon the pressure side when the return line is already open or is openedsimultaneously, this is carried out in the valve control of theinvention by opening the previously closed return line in the presenceof pressure in the cylinder chamber to be supplied, and this is done byopening the relief valve because this type of valve has a substantiallyshorter switching time, eg 60 milliseconds as compared to 150milliseconds for a given amount of flow per second.

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If piston drive is to be actuated in both directions as fast as possibleit is to be understood that each cylinder chamber must have anassociated controlled relief valve in the return line besides theparallel-connected feeding valve in the pressure line. To influence thepiston speed an adjustable quantity limiting valve may be built into theline or lines which serve only for the return travel. In the case of apiston drive which has a piston rod that does not go straight throughthus having unequal piston surfaces, it is recommended to design thedrive in such a way that the cylinder chamber associated with thesmaller piston surface is to be pre-energized, and the cylinder chamberhaving the larger piston surface is to be switched to return travel overthe controlled relief valve in the case of a piston stroke to be rapidlystarted. Otherwise the pressure medium which is under tension from thepressure of the pre-energization would receive a higher pressure thannecessary due to the different size of the piston surface.

An embodiment of the valve control according to the invention for twoparallel-connected work cylinders with straight-through piston rods isshown in the accompanying drawing and is to be applied in a miscutdevice of flying shears where the piston stroke is to be carried out asrapidly as possible in both driving directions.

In reference to the drawing it will be seen that both piston drivesconsist of the cylinders 1, the pistons 2 which are to be pressurecontacted or actuated on both sides and of the straight-through pistonrods 3. In the piston illustrated in the drawing the cylinder chambers1a are to be pre-energized hydraulically according to the principle ofthe invention, and the cylinder chambers 1b are to be unloaded orrelieved for the purpose of starting the piston strokes. The pistonchambers 1a are connected to each other through a line 4 and thecylinder chambers 1b are connected to each other through a line 5, andfrom T-elements 6 and 7 lines 8 and 9 feed into the lines 4 and 5respectively. The lines 4, 8 or 5, 9 constitute pressure lines as wellas return travel lines, depending on the work direction of the pistonrods 3. In front of the T-elements 6, 7 two similar valve controls areassociated with the cylinder chambers 1a or 1b according to theinvention. In a straight continuation of the lines 8 or 9 are locatedthe controlled relief valves 10 and 11 in the lines 14 and 15 servingexclusively for the return travel while the adjustable quantity limitingvalves 12 and 13 are connected ahead of the relief valves are of thetype shown in US. Patent 551,370 and the relief valves may be opened ina known manner by means of threeway valves 16 and 17 hydraulicallyindependently of each other, the three-way valves being connected at theoutlet side over the lines 18 and 19 to the relief valves 10 and 11, andat the input side over the lines 20 and 21 to the common pressure line22, and the lines 23 and 24 to the common return travel line 25.

The uncontrolled relief valves 26 and 27 safeguard the lines 28 and 29which serve exclusively as pressure lines leading from the T-elements 6or 7 to feeding slide valves 30 and 31, which are preferably two-wayvalves. These independently adjustable feeding valves. are connected atthe input side to the common pressure line 22 and are of a known typeincluding a hydraulic-electrical servo control represented by thesolenoids 32 and 33 and the lines 34 and 35 which are constantly underpressure. This servo control is only necessary in connection with heavytwo-way valves 30 and 31 in the case of large amounts of through-flow.

A main pressure line 40 is provided in front of the common pressure line22. Both lines are connected over the line 41 in which a relief valve 42is provided. A disconnectable air-loaded tank 43 which is mountedparallel to line 41 is provided to furnish additional pressure fluid atthe moment when the piston movements are started and absorb any knocksin the pressure lines.

The operation of the valve control according to the invention will nowbe described in reference to the drawing in which all the valves 10, 11,30 and 31, which lie in the main flow of the pressure fluid, are closed.When it is desired that the piston rods 3 should be moved upwardly thetwo-way valve 30 is first opened. In this way the cylinder chambers 1aare put under pressure through the lines 28, 8 and 4 while the pistonrods cannot carry out any movement due to the fact that the cylinderchambers 1b to be relieved are closed over lines 5, 9 and 29 by theclosed relief valve 11 and the closed two-way valve 31. The pre-pressurein line 28 is also safeguarded by means of the closedrelief valve 10.The piston drives are in the pre-energization state or condition.

To start the piston stroke the relief valve 11 is released by openingthe three-way steering slide valve 17. In this Way the connection linebetween the two piston drives is connected to return flow so that thepiston rods 3 are driven forward abruptly under the pre-pressure whichis present in the cylinder chamber 1a.

After the working cycle is terminated the valves 30 and 11 are closedagain. The reversed working cycle is carried out in the same manner bymaking use of the valve 31 for providing the pre-energization of thecylinder chamber 1b and of the valves and 16 for relieving the cylinderchambers 1a.

What is claimed is:

1. A valve control for a reciprocating fluid pressure actuated pistondrive with a rapidly starting piston stroke in at least one directioncomprising, in combination, a fluid pressure actuated cylinder having apiston positioned therein for reciprocating sliding movement, a pistonrod on said piston arranged to be connected to an associated drivendevice, said cylinder having a pair of chambers on opposite sides ofsaid piston, conduit means including valve means connected to saidcylinder chambers for alternately communicating one of said chamberswith an associated source of fluid pressure and the other of saidchambers with associated fluid pressure return means, said valve meansincluding at least one normally closed relief valve for communicatingone of said chambers with said associated fluid pressure return meansand means for selectively opening said normally closed relief valvesubsequent to the communication of said other chamber with saidassociated fluid pressure source and the prepressurizing of said otherchamber for suddenly unloading said one chamber to eifect a rapid strokeof said piston towards said unloaded one chamber, said means for openingsaid normally closed relief valve include auxiliary conduit means havinga three way valve for communicating said relief valve selectively withsaid associated source of fluid and said associated fluid pressurereturn means and means for selectively moving said three way valve intoone position for communicating said relief valve with said associatedfluid pressure return means to permit said relief valve to normallyclose and into a second position for communicating said relief valvewith said associated fluid pressure source for opening said normallyclosed relief valve.

12. A valve control in accordance with claim 1 including an adjustablequantity limiting valve in said conduit means in association with saidnormally closed relief valve for regulating the unloading rate of fluidpressure through said relief valve.

3. A valve control in accordance with claim 1 wherein said rod isconnected to one side of said piston and wherein said cylinder chamberon the other side of said piston communicates through said one normallyclosed relief valve with said fluid pressure return means.

4. A valve control in accordance with claim 1 wherein a pair of saidnormally closed relief valves are provided in said conduit means, eachof said relief valves being associated with one of said cylinderchambers for alternately communicating said cylinder chambers with saidfluid pressure return means and wherein means for opening said normallyclosed relief valves are provided for each of said relief valves foralternately opening said relief valves to suddenly unload one of saidchambers subsequent to the communication of the other of said chamberswith said associated fluid pressure source and the pre-pressurizing ofsaid other chamber to effect a rapid stroke of said piston in bothdirections of said reciprocating movement.

CARROLL B. DORITY, IR., Primary Examiner.

U.S. Cl. X.R.

